SAN DIEGO - Federal prosecutors on Tuesday dropped corruption charges against the longtime former head of the union representing Border Patrol agents, 18 months after accusing him of defrauding the organization out of hundreds of thousands of dollars.

U.S. District Judge William Hayes agreed to the government's request to dismiss nine counts of conspiracy and fraud against Terence J. Bonner one day before a key hearing to determine what evidence would be allowed at trial. The decision followed a series of pretrial setbacks for prosecutors, including a ruling that that they cannot use pornographic images and other evidence seized from computers in Bonner's home.

Bonner, former president of the National Border Patrol Council, said the prosecution was "pure political retribution" for his outspoken positions against immigration and law enforcement policies.

"I feel relieved, but at the same time I feel violated, for lack of a better word," he said in an interview. "I've undergone four years of hell, where they've dragged my name through the mud and made baseless allegations against me. ... It was a message they were sending against anyone who speaks out against the policies of the government."

Prosecutors said the pretrial rulings caused them to seek dismissal of the charges.

"The grand jury found probable cause that Mr. Bonner had committed the offences set forth in the indictment," said U.S. Attorney Laura Duffy. "From time to time in criminal cases certain evidence is suppressed for legal or technical reasons. We respect the process and the court."

Bonner, 60, was the union's president from 1989 until he retired in 2011 â€” a period of major growth in U.S. border enforcement. The indictment says he represented more than 14,000 agents and other employees who paid monthly dues of $56 to the union, which is part of the American Federation of Government Employees and AFL-CIO.

Bonner, widely known as T.J., was a fixture on cable television and in congressional hearings. News reporters often turned to him for critical commentaries on immigration enforcement policies even after he retired.

In August 2012, prosecutors accused him of submitting expense vouchers for meals, car rentals, luggage, books and other activities when he was travelling for personal reasons. The indictment said his false claims cover periods when he was visiting a mistress in Chicago, his family, hockey games and other sporting events unrelated to the union.

Prosecutors refiled charges in September after the judge ruled much of the evidence inadmissible. The judge scheduled an evidentiary hearing only five days before Bonner was to go on trial last week.

The two-day hearing to further consider what evidence would be allowed was scheduled to begin Wednesday and was to include questioning and cross-examination of witnesses. Bonner's attorney, Eugene Iredale, planned to argue that the case relied on evidence that was obtained outside the scope of a search warrant executed in March 2012 at Bonner's home in Campo, about 60 miles east of San Diego.

Bonner said the judge's decision to order the hearing was the prosecution's "death knell."

"This case has consumed my life in all of my waking moments and caused me many sleepless nights," he said. "It has taken an emotional and financial toll on me and pushed me to the edge of bankruptcy. You wonder what it is wrong with our system of justice."

The National Border Patrol Council's current leadership has distanced itself from Bonner, saying after charges were filed that it adopted tighter internal controls.

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